The light-emitting mechanism of the LED is to release energy generated from the energy gap between an n type semiconductor layer and a p type semiconductor layer by emitting photons thereafter. Because the above mechanism is different from the lighting mechanism of the light bulb, the light-emitting device is named cold light source. Moreover, LED also shows significant improvement in liability, lifetime, flexible application and power saving. Therefore, LED is a long-excepted innovation in the light source industry and considered as one of the preferred lighting device for the next generation.
FIG. 1 is a structure diagram of a conventional light-emitting diode. As shown in FIG. 1, a conventional light-emitting device 100 comprises a conductive substrate 10, a metal adhesive layer 12 disposed on the conductive substrate 10, an omni-directional reflector layer 14 disposed on the metal adhesive layer 12, an ohmic contact layer 15 disposed on the omni-directional reflector layer 14, a light-emitting stack layer 16 disposed on the ohmic contact layer 15, and an electrode 18 disposed on the light-emitting stack layer 16 wherein the ohmic contact layer 15 can be a transparent conductive material such as a transparent conductive oxide layer or a thin metal.
In the conventional light-emitting device 100, the light-emitting stack 16, from top to bottom, comprises a first conductive semiconductor layer 160, a light-emitting layer 162 and a second conductive semiconductor layer 164. The omni-directional reflector layer 14 further comprises a metal reflective layer 140 and a low refractive index layer 142 having lower refractive index comparing with metal reflective layer 140, wherein the material of the metal refractive layer 14 can be Au and Silver, and the material of the low refractive index layer 142 can be SiO2 and Indium Tin Oxide (ITO). In addition, the omni-directional reflector layer 14 further comprises a plurality of ohmic contact dots 144 penetrating through the low refractive index layer 142, and electrically connecting with the ohmic contact layer 15 and the metal refractive layer 140 respectively to conduct current flow so that the electrical performance of the conventional light-emitting device 100 is improved.
However, during the manufacturing process of the above light-emitting diode 100, high thermal processing would incur reaction between the ohmic contact layer 15 and the low refractive index layer 142 of the omni-directional reflector layer 14, and therefore decrease brightness efficiency of the light emitting diode 100. Moreover, the ohmic metal contact point 144, disposed for increasing electrical conductive characteristic of the light-emitting diode 100, is likely to absorb lights emitted from the light emitting layer 162 so as to decrease the lighting efficiency of the light-emitting diode 100.
Besides, the light-emitting device 100 can be combined with other elements to form a light-emitting apparatus. FIG. 4 is a diagram of a conventional light-emitting apparatus. As shown in FIG. 4, a light-emitting apparatus 600 comprises a sub-mount 60 having at least a circuit 602, one solder 62 and an electrical connecting structure 64. The solder 62 is disposed on the sub-mount 60 so as to bond the light-emitting device 100 to the sub-mount 60 and electrically connect the substrate 10 of the light-emitting device 100 with the circuit 602. The electrical connecting structure 64 electrically connects the electrode 18 of the light emitting diode 100 with the circuit 602 of the sub-mount 60 wherein the sub-mount 60 can be a lead frame or a mounting substrate for the purpose of circuit arrangement and heat dissipation.